In some catheterization techniques, it is desirable to use a series of catheters in order to complete effectively the procedure at hand. For example, in percutaneous transluminal coronary angioplasty procedures, in which a balloon catheter is advanced into an obstructed (stenosed) region of the patient's coronary artery and is inflated within the stenosis to dilate the lumen of the artery, it is not uncommon for the physician to require the sequential use of several balloon dilatation catheters having balloons of progressively increasing size. Typically, such catheters are used in connection with a guidewire that extends through the catheter and serves as a guide over which the catheter may be advanced to the stenosis. When performing such a catheter exchange, it is important to do so without shifting and losing the position of the guidewire so that the guidewire may be used to guide the next catheter to the stenosis.
In order to maintain guidewire position during a catheter exchange, conventional practice has been to use a relatively long exchange wire. The exchange wire, which typically is of the order of 300 cm long (as compared to a conventional guidewire length of the order of 180 cm), is first exchanged for the conventional indwelling guidewire by removing the indwelling guidewire from the existing catheter and replacing it with the longer exchange wire. Then the existing catheter is withdrawn over the exchange wire, the exchange wire being sufficiently long so that it is never completely covered by the withdrawn catheter, thereby enabling the exchange wire to be held in position by the physician or an assistant during the catheter withdrawal. After the initial catheter is removed, the succeeding catheter is advanced over the exchange wire which guides the second catheter to the stenosis. The exchange wire then may be removed and may be replaced with a conventional guidewire which, typically, will be more easily manipulated during the angioplasty procedure.
The foregoing procedures are time consuming and somewhat awkward. A significant advance in the technique for effecting catheter exchanges has been developed and involves a system that enables exchange of catheters without using exchange wires. In brief, that system utilizes an extension wire that is attached to the proximal end of the guidewire already in place in the patient. That effectively extends the overall length of the guidewire to that needed for the catheter exchange. The system is described in U.S. Pat. No. 4,917,103 issued Apr. 17, 1990 (Gambale). It uses a connection in which the distal end of an extension wire is telescoped together with the proximal end of the guidewire and the junction then is crimped, thus, retaining the wires together. With the crimped connection, when the guidewire and extension wire are detached, their reconnection is impaired because of the deformation formed during their connection. Thus, some inconvenience is presented should it be desirable to make multiple catheter exchanges.
Several devices have been designed for enabling reconnectible detachment of the guidewire and extension. Such devices are disclosed in U.S. Pat. No. 4,827,941 (Taylor) and in European Patent Application 89304257.2 published Dec. 20, 1989 (Palermo). The Taylor device discloses a connector for a guidewire and guidewire extension in which one of the members is provided with a tubular socket at one mating end and the other member is provided, at its mating end, with a serpentine like, undulating male member insertable into the socket. The diameter defined by the socket is less than the diameter defined by the male element so that the male element can be forced into the tubular element and be retained in the tube by friction. Among the difficulties with this arrangement is that the connector elements may not be retained together with the degree of security that may be desired. The extent to which the frictional forces retain the male element and socket together is limited by the maximum permitted connection force. The connection forces necessarily are limited because the parts are very small and delicate and could become damaged if too great a force were applied to them. It is not uncommon for the guidewire and guidewire extension, so connected, to become separated, either from manipulation of the guidewire or by being dragged apart by a catheter during removal of the catheter is a catheter exchange.
The invention described in the above mentioned European patent application (Palermo) provides a still further improvement in that the connection between the guidewire and extension includes a male member insertable easily and under low force into a receptive socket. The connection, however, is not a frictional connection but rather results in a mechanical interlock that will not separate when subjected to axial tension. More specifically, the connection system utilizes a telescoping connector that is self latching, disconnectible and reconnectible without deformation of the guidewire or the extension. In this arrangement the guidewire is provided with a tubular socket on the proximal end. The extension wire includes a shaft having a distal end that is surrounded by a helical coil, formed from rectangular cross section wire. The coil is attached to the extension wire shaft at the distal end of the coil and is free at the proximal end of the coil to enable the coil to stretch and contract about the shaft. The distal end of the extension wire carrying the coil is easily insertable under low force into the socket on the proximal end of the guidewire but self-locks in the socket and cannot be easily withdrawn. Application of axial tension to the guidewire and extension wire causes the edges of the rectangular cross-section wire to mechanically dig into the inner surface of the socket, thus precluding separation of the guidewire and extension wire. The extension wire and guidewire may be disconnected easily, however, by twisting the guidewire extension while simultaneously withdrawing it axially from the socket. The twisting motion frees the locking engagement of the helical coil with the internal surface of the socket.
Although the Palermo device represents a significant improvement it nevertheless presents some limitations. The structural configuration of the coil is such as to impose practical lower limits on the size of guidewire and extension with which that connection can be used. In particular, it has been found to be difficult to use the coil-type of connection with guidewires smaller than 0.014" in diameter. Another difficulty that sometimes has been encountered is that when the physician's hands (wearing surgical gloves) become wet, as is common during an angioplasty procedure, it may be difficult to get a sufficient grip on the small diameter guidewire extension to twist it in order to free the locking engagement of the coil.
It would be desirable, therefore, to provide a guidewire and extension system having the attributes and advantages of the Palermo system but in an arrangement capable of use with smaller diameter guidewires. It also would be desirable to provide such a guidewire extension system in which the unlocking of the guidewire extension to the guidewire can be effected more easily. It is among the objects of the invention to provide such an improved device.